Iron alloy



United States Patent 3,170,824 IRON ALLOY Donald B. Roach, Dimon A. Roberts, and Albert M. Hall,

Columbus, Ohio, assignors to the United States of Americe as represented by the United States Atomic Energy Commission No Drawing. Filed Dec. 27, 1962, Ser. No. 248,187

4 Claims. (Cl. 148-31) This invention deals with an iron-base alloy, and more particularly with a manganese-, nickeland carbon-com taining steel.

For a great number of applications, alloys that have a high degree of ductility and great toughness are desir- 3,170,824 Patented F eb. 23, 1965 Ice.

If a material is work-hardened rapidly during tensilestressing, high values both of uniform and total elongation are obtained. The austenitic stainless steels, which work-harden rapidly, will tend to show enhanced ductility i TABLE I Typical strength and ductility properties of various commercial alloys Ultimate 0.2% Ofiset Total Material Composition Condition Tensile Yield Elonga- Strength, Strength, tion in 2',

p.s.i. p.s.i. percent A181 1010 carbon steel 0.10% 0 Hot rolled. 51, 000 29, 000 38 A181 301 stainless steel 0.15% 17% Cr, Annealed.-. 105, 000 40, 000 55 AIS]: 816L stainless steel at (i 16% Cr, .d0 85,000 30, 000 55 .usr 430 stainless steel 0.12%? C, '16%or 75, 000 40, 000' Yellow brass u, N1.: 46, 000 g 14, 000 65 Phosphor bronze 92% 11, 8% Sn....'.. 55,000 24, 000 70 Wrought Hadfield Steel ing-1 /14% 131, 000/102, 000 50, 000/60, 000 40/60 Wrought Modified Hadfield Steel 1.1/1.4% C, 10/14% 130, 000/155, 000 50, 000/63, 000 48/72 Mn, sea 3.7575011.

able. This is particularly true for specific steels and alloys that are to be fabricated into complex shapes, such as by deep-drawing. Another important requirement for such steels, especially when used for structural elements, is the ability to deform under excessive stress or loading instead of failing due to brittleness. Materials which show high ductility, as measured by reduction in area in the tension test, are not necessarily materials that can undergo severe forming operations or withstand high service stresses in the presence of notches, because high tensile reduction of area is really a measure of high plastic instability.

In most instances, ductility is measured by the total elongation within a 2-inch gage length in the tension test. This also is somewhat misleading in that only that part of the elongation is useful, either in forming operations or in service, which is uniform or occurs before necking (plastic instability) commences. It is believed by many that the uniform elongation before necking is the real measure of useful ductility.

For many applications, existing materials do not eX- hibit sufiiciently uniform elongation, or even not sufiicient total elongation, to accomplish the desired forming operations. In addition, many high strength structural materials lack toughness in the presence of notches to satisfy service requirements.

It is an object of this invention to provide steels that have high yield and tensile strengths, exceptionally uniform elongation and ductility, a high degree of notch toughness and excellent energy dissipation characteristics without failure.

Table I lists various known commercial materials which exhibit so-called good ductility (determined on 0.505- inch-diameter tension test bars). Of these common materials those which have high ductility have a face-centered cubic structure (austenitic); these are the copper-base up to the point where the austenite transforms under strain to hard martensite; at this point, however, further work-hardening during straining is disadvantageous, since plastic instability sets in and necking occurs.

When the austenite stability of austenitic steels is increased to such an extent that the formation of martensite during tensile-straining is greatly retarded, the uniform elongation values are also increased. This has been found to be true for iron-manganese-carbon steels, commonly known as Hadfield steels. It is known that the austenite in the standard Hadfield manganese steels tends to transform to martensite after about 50 to 60 percent elongation, giving rise to plastic instability and failure. Uniform elongation values exceeding 60 percent and total elongation values exceeding 70 percent are seldom found in Hadfield manganese steels.

We have found that by the addition of considerable amounts of nickel together with a proper control of the carbon content and by annealing of the alloy at about 1100 C. followed by quenching in water, uniform elongations before necking can be produced that are far superior to any values heretofore obtained in known alloys. We have found that by adding at least 7 percent by weight of nickel, preferably from 7 to 11 percent, to a steel containing from 13 to 18 percent by weight of manganese and from 0.95 to 1.1 percent of carbon, uniform elongations of greater than percent and total elongations of above percent and even up to percent are obtained. The preferred manganese content is one between 14 and 15%, and the silicon content may range up to 1%.

The steels of this invention thus contain from 13 to 18 percent by weight of manganese, from 7 to 11 percent by weight of nickel, and from 0.95 to 1.10 percent by weight of carbon.

.1; Typical properties of steels of this invention are given in Table II.

TABLE II Strength and ductility properties of Fe-Mn-Nl-C steels Nominal Com- Tensile Properties position, Percent Alloy Elongation N0. Ultimate 0.2 Percent Tensile Ofiset M11 Nl Strength, Yield Uni- Total p.s.i. 1tl- Strength, form in 2,

p.s.i. 10- in 1, Percent Percent 14. 0 7. 0 124. 9 47. 0 82. 93. 0 14. O 9. 0 125. 9 45. 0 Q0 94. 5 14. 0 11. 0 122. 5 46. 3 81. 5 95. 0 14. 0 7. 0 135. 4 48. 8 92 09. 0 14. 0 9. 0 133. 8 49. 2 88. 0 93. 0 14. 0 11.0 135. 4 51. 1 94. 5 102. 0 14. 0 7. 0 144. 9 52. 7 94. 5 100. 0 14. 0 9. 0 141. 3 52. 4 93. 5 97. 5 14. 0 l1. 0 137. 8 53. 6 83. 0 8 8.- 0 14. 0 7. 0 154. 2 65. 6 83. 5 85. 0

The ability of the alloys of Table II to absorb energy is well manifested, for instance, by Charpy V-notch impact tests carried out on Alloy 4 (0.95 percent C, 14 percent Mn, 7 percent Ni); this steel had the unusually high Charpy value of 165 ft. lbs. when tested at room temperature.

In making the alloys of this invention, iron and nickel were first melted together in a magnesia crucible in an induction furnace. The desired quantity of ferro-manganese, with or without ferrosilicon, was then added. After a homogeneous melt had been obtained, the alloy was deoxidized by the addition of about 0.05 percent by weight of aluminum. The melted metal was then cast into a copper mold; sound bodies were always obtained. The alloy was then heated to about 1100 C. for 30 minutes and forged to I A-inch-thick square bars. These bars were then hot-rolled at the same temperature to cylindrical bars of a diameter of Ms inch; they were finally straightened and quenched in water after annealing at 1100 C. Other methods, of course, can also be used.

For the tensile tests the bars were rough-machined to %-inch diameter; any decarburized surface material was removed thereby. The specimens were then turned to a final diameter of half an inch.

Tensile strength, yield strength and elongation values were determined in all cases after annealing at 1100 C.

for 30 minutes followed by quenching in water. The results are entered in Table 11; all values are averages of two parallel tests.

In two steels containing the same amount of carbon but different quantities of nickel, a higher total elongation was obtained with the higher nickel content; on the other hand, the steels having the higher nickel content yielded the best results with the lower carbon content of about 0.95%. A carbon content of 0.80%, for instance, proved not high enough for optimum elongation, while a carbon content of 1.1% was found to be too high with a nickel content of 11% to yield optimum results, although still superior to the steels used heretofore. The tensile and yield strengths were not very much affected by a change in either carbon or nickel content. The data of the table are slightly erratic, which is usual and due to analytical error; however, reproducibility of the properties cited has been very good. The improvement is clearly evident when the various characteristics are compared with the corresponding values of known steels shown in Table I.

It will be understood that the invention is not be be limited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. As a new composition of matter, a highly ductile alloy annealed at about 1100" C. and water-quenched, said alloy consisting of from 13 to 18 percent by weight of manganese, from 7 to 11 percent of nickel, from 1.1 to 0.95 percent of carbon and up to 1 percent of silicon, the balance being iron.

2. The alloy of claim 1 wherein the manganese content is between 14 and 15 percent.

3. An iron alloy containing 0.95 percent by weight of carbon, 14 percent of manganese and 11 percent of nickel, heat-treated at about 1100 C. and water-quenched.

4. An iron alloy containing 1.10 percent by weight of carbon, 14 percent of manganese and 7 percent of nickel, heat-treated at about 1100 C. and water-quenched.

References Cited by the Examiner UNITED STATES PATENTS 1,435,840 11/22 Hadfield 148l37 X OTHER REFERENCES Revue de Metallurgie, Tome 2, 1905, Memoires, page DAVID L. RECK, Primary Examiner. 

1. AS A NEW COMPOSITION OF MATTER, A HIGHLY DUCTLE ALLOY ANNEALED AT ABOUT 110*C. AND WATER-QUENCHED, SAID ALLOY CONSISTING OF FROM 13 TO 18 PERCENT BY WEIGHT OF MANGANESE, FROM 7 TO 11 PERCENT OF NICKEL, FROM 1.1 TO 0.95 PERCENT OF CARBON AND UP TO 1 PERCENT OF SILICON, THE BALANCE BEING IRON. 